Equine Viral Arteritis (EVA)
By Karen Laden
It's the big day: time to breed the terrific twosome. Everyone's thoughts turn to the lovely foal this outstanding mating will produce in 11 months.
Then Equine Viral Arteritis (EVA) silently enters the breeding shed. The unsuspecting stallion owner and mare owner have just unleashed a potential epidemic on all the breeding farms of their clients, friends and
"There must be increasing awareness of the disease and the consequences of the infection; the potential for abortions, the carrier state in stallions and young foals dying," said Peter Timoney, MVB, PhD, FRCVS, chairman of the Department of Veterinary Science at the Gluck Equine Research Center at the University of Kentucky.
"Stallion owners and managers are going to become increasinglyresponsible that (stallions) be tested, confirmed non-carriers and vaccinated. That is coming. Broodmare owners will be more careful to confirm that stallions are EVA negative and vaccinated after last year's multi-state outbreak," he said.
Timoney, a native Irishman, is designated as a world specialist on EVA by the Office International des Epizooties or World Animal Health Organization. He recently stepped down as the longtime director of the Gluck Center to spend more time on research.
Based on Timoney's research and writings, here is how EVA, a contagious viral infection, typically dominos through a breeding farm:
-- A colt/stallion contracts EVA, primarily through the nasal discharge of an EVA-infected equine. The colt/stallion recovers, but the virus remains in the reproductive tract where it constantly sheds in the semen, making the colt/stallion a silent EVA-carrier. This carrier stallion now can infect the mares to which he is bred, whether through live cover, shipped cooled or frozen semen. As many as 70 percent of the infected mares will abort their foals; the foals that go full term usually will die within a few days of birth.
-- Each EVA-infected pregnant mare now passes the virus, primarily through nasal discharge, to all the equines with which she comes into contact. The result: additional abortions and newborn deaths as well as the death of very young infected foals, due to pneumonia. If this EVA-infected mare transmits the virus to a colt/stallion, odds are high that a new carrier stallion is created to continue the deadly cycle.
So just keep your stallions, broodmares, young foals and colts away from equines with runny noses and they will be safe, right?
Wrong. EVA-infected equines often show no signs of sickness. Or the signs may look as if they stem from some other cause.
According to the USDA Animal and Plant Health Inspection Service's EVA Fact Sheet, if an EVA-infected equine does exhibit clinical signs, they may include one or all of the following: fever, nasal discharge, loss of appetite, respiratory distress, skin rash, muscle soreness, conjunctivitis, depression, swelling around the eyes, ocular discharge, swollen limbs, swollen genitals in stallions and swollen mammary glands in mares. A simple blood test is the best way to diagnose EVA.
Although EVA outbreaks and epidemics occur rather infrequently in the US, just one carrier stallion can wreak havoc on an entire breeding season for both large and small breeders alike.
The first reported EVA case in the US followed an extensive outbreak in 1953 on an Ohio Standardbred farm. In 1984, the virus reached epidemic proportions in Kentucky with one carrier stallion affecting 41 Thoroughbred
In 2006 the virus struck the Quarter Horse industry. As a result, 18 states implemented quarantine restrictions. Nine of those states reported positive EVA cases. The virus was traced back to just one Quarter Horse breeding farm.
EVA also has been introduced into the US Warmblood population through the import of both infected frozen semen and carrier stallions. Europe has struggled with the virus since the mid-nineteenth century, when it was
first described in veterinary literature.
All but very young equines recover from EVA without any veterinary care. Previously infected broodmares also won't abort in subsequent years unless they are re-infected due to a lack of immunity. However, there is no
cure for EVA-carrier stallions.
Yet, experts agree that EVA is a very manageable disease - that eventually could be eradicated - by following the proper vaccination protocol. The first step is blood testing to insure that the equine, especially a stallion, is EVA negative, but blood testing alone is not enough.
"A stallion with a negative blood test is nearly as vulnerable to infection as other animals under risk management analysis. I see no reason not to implement a vaccination program and revaccinate annually to protect a stallion," Timoney said. "We have a good, safe, vaccine that is very effective."
According to Timoney, the modified live virus vaccine, introduced by Fort Dodge Animal Health in 1985, shows no evidence of causing a vaccinated stallion to shed EVA in its semen or make the stallion an EVA carrier.
Timoney recommends vaccinating colt foals between six and 12 months of age, open broodmares at least two months before breeding, and mature stallions at least four weeks before the start of breeding season. Only vaccinated mares should be bred to carrier stallions.
"If a stallion is already a carrier, the vaccine will not stop the stallion from shedding EVA in its semen," said Tom Lenz, DVM, vice president of professional services at Fort Dodge Animal Health in Overland Park, Kansas.
"You have to make sure with stallions that they are blood tested for their status before they are vaccinated."
Equines receiving their first vaccination must be isolated for 21 days, since they will shed the virus and could infect other animals, Lenz said, but no quarantine is required for the annual booster. The booster is required,
he said, because the immunity does not last. "With natural exposure, the immunity lasts only a few years."
Timoney said breeders also need to educate themselves about the import and export rules regarding equines that have been vaccinated for EVA. If properly documented, most countries now allow the importation of
EVA-vaccinated equines and their semen. However, the US is the only country that allows carrier stallions and EVA-positive semen from non-vaccinated stallions to enter its borders.
Claudia Friedrichs, operations agent for International Racehorse Transport (IRT) in Chicago, Ill., said, "When exporting vaccinated ponies, they must have the documentation to show negative EVA prior to the vaccination." She recommends always contacting an equine export company to learn the import rules of a specific country before finalizing a sale to that country.
For additional information about EVA, visit these websites:
Note: This article does not replace the knowledge and advice of a qualified veterinarian.
Published in the July/August 2007 issue of the 'American Connemara' magazine. Article updated 3/8/2008. copyright Karen Laden, Kingswell Connemaras; can be used with written permission
*Smaragaid Cliff, standing at Kingswell Connemaras, tested EVA negative in 2007 and has been vaccinated annually. His paperwork is on file with the State of Colorado Veterinarian's Office and the American Connemara Pony Society.
"The Lord is good to all; he has compassion on all he has made." Psalm 145:9